Correct typo, add "gut" mainly to ease searching later

README.md

@@ -441,7 +441,7 @@ This section includes information about so-called "long COVID".
 * [Post-hospitalisation COVID-19 study (PHOSP-COVID)](https://www.phosp.org/), recruiting 10,000 patients who have been hospitalised with COVID-19 in the UK
 * [CORAL Study](https://www.thecoralstudy.com/about), trying to understanding the impact of COVID-19 on young people, adults, pregnant women and older people to predict need for mental health support
 * [Study to identify markers that could predict COVID-19 outcome](http://www.bristol.ac.uk/news/2020/may/discover-study.html) by the University of Bristol finds that [Three quarters of patients report long-term effects of coronavius](https://www.bristol.ac.uk/news/2020/august/discover-study-findings.html)
-* [Evolution of antibody immunity to SARS-CoV-2](https://www.nature.com/articles/s41586-021-03207-w) finds that in a cohort of 87 patients 10% of which needed hospital care, 44% reported long-term symptoms after 6 months, and it also suggests that there may still be replicating virus in the intesting of about half of infected individuals at least 90 days after infection (see also [this tweet](https://twitter.com/profshanecrotty/status/1365107289011539970) commenting about that)
+* [Evolution of antibody immunity to SARS-CoV-2](https://www.nature.com/articles/s41586-021-03207-w) finds that in a cohort of 87 patients 10% of which needed hospital care, 44% reported long-term symptoms after 6 months, and it also suggests that there may still be replicating virus in the intestine (gut) of about half of infected individuals at least 90 days after infection (see also [this tweet](https://twitter.com/profshanecrotty/status/1365107289011539970) commenting about that)
 * [Persistent Symptoms in Patients After Acute COVID-19](https://jamanetwork.com/journals/jama/fullarticle/2768351), an Italian study on patients that were hospitalized, after around 60 days
 * [The prevalence of long COVID symptoms and COVID-19 complications](https://www.ons.gov.uk/news/statementsandletters/theprevalenceoflongcovidsymptomsandcovid19complications), by the British [Office for National Statistics](https://www.ons.gov.uk/), has plans for estimating the prevalence of, and risk factors for, "long COVID" symptoms and health complications following coronavirus (COVID-19) infection, and early data
 * [Outcomes of Cardiovascular Magnetic Resonance Imaging in Patients Recently Recovered From Coronavirus Disease 2019 (COVID-19)](https://jamanetwork.com/journals/jamacardiology/fullarticle/2768916), a study on 100 "unselected" patients in Germany (median age 49), finds that 78% had cardiac involved, and 60% ongoing myocardial inflammation