[generator] Document how to use the generator in a fork

[kakwa]

When fixing the generator (patchs.go fixes), a contributor needs to build the local patched version.

However go build -o generator github.com/IceflowRE/go-wargaming/v4/tools/generator (like instructed in the README) will build the unpatched version from the upstream repository, not the local checkout.

It's possible to build the generator locally (go build -o generator tools/_generator/main.go, but it has other side effects, mainly messing-up the imports:

 import (
-       "github.com/IceflowRE/go-wargaming/v4/wargaming/wgnTime"
+       "/wargaming/wgnTime"
 )

Put also adding // spacing comment lines:

 // realm:
-//     Valid realms: RealmAsia, RealmEu, RealmNa
+//
+//     Valid realms: RealmAsia, RealmEu, RealmNa
+//
 // search:
-//     Player name search string. Parameter "type" defines minimum length and type of search. Using the exact search type, you can enter several names, separated with commas. Maximum length: 24.
+//
+//     Player name search string. Parameter "type" defines minimum length and type of search. Using the exact search type, you can enter several names, separated with commas. Maximum length: 24.

My go version:

> go version
go version go1.19.8 linux/amd64

[IceflowRE]

Woops. Will take a look.

[IceflowRE]

I could not reproduce the local build failure.
If i do

go build -o generator github.com/IceflowRE/go-wargaming/v4/tools/_generator

it will build from the local version.
Probably you had the newest version and did

go build -o generator github.com/IceflowRE/go-wargaming/v4/tools/generator

Note the missing underscore. I added the underscore, that the tools wont be delivered when doing go get. This might have been the issue here.
Will update the readme.

[IceflowRE]

The generator generation should be correct now. The formatting is continued here #8 .
If i am wrong please reopen, with additional information.