Update comparison with sed

Mention the `-E` flag for `sed`, but with some caveats, to make the comparison more fair. Split out the delimiter quoting from the slash quoting examples, and pick an example that's more favorable for `sd`. Add a simple example just comparing the noisier syntax of `s///g` vs two arguments. Add an example of the danger of `sed -i` in cross-platform usage.

README.md

@@ -23,16 +23,26 @@ Find & replace expressions are split up, which makes them easy to read and write
 While sed does a whole lot more, `sd` focuses on doing just one thing and doing it well.
 
 Some cherry-picked examples, where `sd` shines:
+
+- Simpler syntax for replacing all occurrences:
+  - sd: `sd before after`
+  - sed: `sed s/before/after/g`
 - Replace newlines with commas:
   - sd: `sd '\r' ','`
-  - sed: `sed ':a;N;$!ba;s/\r/,/g'`
-- Extracting stuff out of strings with special characters
-  - sd: `echo "{((sample with /path/))}" | sd '\{\(\(.*(/.*/)\)\)\}' '$1'`
-  - sed
-    - incorrect, but closest I could get after 15 minutes of struggle
-    - `echo "{((sample with /path/))}" | sed 's/{((\.\*\(\/.*\/\)))}/\1/g'`
-
-Note: although `sed` does have a nicer regex syntax with `-r`, it is a non-portable GNU-ism and thus doesn't work on MacOS, BSD, or Solaris. 
+  - sed: `sed ':a;N;$!ba;s/\r/,/g'`, or use a different tool like `tr`.
+- Familiar regex syntax by default:
+  - sd: `echo "start middle end" | sd 'start (.+) end' '$1'`
+  - sed: basic REs have an unfamiliar and limited syntax, `-E` for more familiar syntax of extended regular expressions is widely supported but not available on some platforms like Solaris:
+    - `echo "start middle end" | sed 's/start \(..*\) end/\1/g'`
+    - `echo "start middle end" | sed -E 's/start (.+) end/\1/g'`
+- Extracting stuff out of strings containing slashes:
+  - sd: `echo "sample with /path/" | sd '.*(/.*/)' '$1'`
+  - sed: you need to know that the delimiters for `s` can be replaced with other arbitrary characters
+    - `echo "sample with /path/" | sed -E 's|.*(/.*/)|\1|g'`
+- In place modification of files:
+  - sd: `sd before after -i file.txt`
+  - sed: you need to be careful to use `-e` or else some platforms will consider the next argument to be a backup suffix
+    - `sed -i -e 's/before/after/g' file.txt`
 
 ## Installation